Robert C. Whitmore

Structural Characteristics of Grasshopper Sparrow Habitat

Based on data from Breeding Bird Survey routes, the grasshopper sparrow (Ammodramus savannarum) has declined in West Virginia (Whitmore and Hall 1978). In much of the mid-Appalachians, surface-mine reclamation procedures have created large tracts of grassland that have potential for use by grasshopper sparrows (Allaire 1978, Whitmore 1978, Whitmore and Hall 1978). Because of the availability of this new habitat, grasshopper sparrows have become locally common in West Virginia, reaching population densities of 120 pairs/100 ha (Whitmore 1979). Because little was known about grasshopper sparrows (Smith 1963), my study was designed to quantify their habitat requirements, with special reference to key aspects of vegetation structure. The procedures outlined could serve as a basis

Indirect effects of gypsy moth defoliation on nest predation

Large areas of forested land are altered each year from gypsy moth (Lymantria dispar) larvae feeding. Little is knovrn about the impacts of forest defoliation on populations or reproductive success of forest-dwelling birds. Therefore, we investigated the effects of defoliation by gypsy moth larvae on the vulnerability of artificial bird nests to predation. We placed 450 nests along transects in a West Virginia oakhickory (Quercus/Carya spp.) forest that had received variable defoliation for 3 years. Nests placed in defoliated sites suffered a bigher predation rate (41.6%) than did those in nondefoliated sites (22.7%, P = 0.001). Nests placed ≤1 m from the ground suffered higher predation than those placed >1 m (46.4 vs. 21.7%, P < 0.001)

Dietary Shifts Among Songbirds From a Diflubenzuron Treated Forest

Effects of diflubenzuron (a chitin-synthesis inhibiting insecticide) application on diets of forest birds were evaluated in eastern West Virginia in 1986. Nine species of songbirds were collected from May through July from treated and untreated plots. Gut contents from each specimen were removed and 10 arthropod taxa were identified. The percentage biomass comprised by each food taxon and total gut biomass was determined for each specimen. The diets of five species were significantly different between treated and untreated plots. In general, biomass of Lepidoptera larvae was reduced and biomass of other orders (Homoptera, Diptera, Coleoptera, etc.) was greater at treated sites. In addition, two species displayed reduced total gut biomass at treated sites. These data show that while diflubenzuron is not directly toxic to vertebrates, birds are affected indirectly through reduced availability of Lepidoptera larvae. Birds possessed differing capabilities to compensate for these diflubenzuron-induced food reductions. Most birds adjusted by switching prey, while others consumed less food. Resident species experienced less impact than did migrants.

Food habits of the endangered Virginia big-eared bat in West Virginia

Food habits of the endangered Virginia big-eared bat ( Plecotus townsendii virginianus ) were determined by analyzing guano and culled parts of insects collected in 1988 and 1989 from three maternity caves in eastern West Virginia. Food availability was evaluated by lighttrapping at forest edge and forest interior sites in the vicinity of the caves. Lepidoptera was the most important insect order in the diet, followed by Coleoptera, Diptera, and Hymenoptera. Significant differences among bats from the different caves were observed in the percentage volume and frequency of Lepidoptera, Coleoptera, Diptera, and Hymenoptera. Bats selectively consumed Lepidoptera and avoided Coleoptera. Volume and frequency of Lepidoptera, Hymenoptera, and Coleoptera in the diet were positively related to their abundance in the forest interior. Patterns of consumption of Diptera paralleled abundance at the forest edge. Lepidoptera wings accounted for 90% of culled insect parts, 70% of which were from larvae that developed in forests.

Multivariate measures of niche overlap using discriminant analysis

Abstract Two measures of multivariate niche overlap defined on p resource variables are presented. By measuring the niche overlap on the discriminant variable the multivariate problem is reduced to a univariate problem while preserving the relevant multivariate information. The niche overlap is then calculated by two different techniques. The first technique uses the MacArthur-Levins (Amer. Natur. 101, 377–385, 1967) measure for probabilities of joint occurrence, while the second computes the density overlap of two use curves. An illustration of the multivariate approach to actual field data is demonstrated.

Comparison of Two Double‐Observer Point‐Count Approaches for Estimating Breeding Bird Abundance

Abstract Point counts are one of the most widely used and efficient approaches to survey land-bird populations. A new approach to point-count surveys involves the use of 2 observers, which allows the calculation of a detection probability for each bird species. Detection probabilities derived from 2 observers permit investigators to calculate a corrected abundance estimate that accounts for birds present but not detected. We evaluated 2 double-observer point count approaches: the dependent-observer approach and the independent-observer approach. The dependent-observer approach involves 2 observers recording data together on a single data sheet with one observer designated the primary observer and the other designated as the secondary observer. The primary observer verbally dictates the number of each species detected while the secondary observer records this information; the secondary observer also records birds that the primary observer did not detect. The independent-observer approach involves 2 observers recording data independently on separate data sheets without verbal communication between observers. This study compares the detection probabilities and associated levels of precision generated by both double-observer approaches to ascertain which technique generates data that are more accurate and more feasible to apply in the field. We conducted point counts at 137 point locations in northern West Virginia during the spring of 2000 and 2001 using both double-observer approaches. We generated detection probabilities and abundances from data collected using both double-observer approaches using program DOBSERV. The dependent-observer approach resulted in higher observer-specific and joint detection probabilities, as well as lower standard errors of detection probability across most cover types. Species-specific detection probabilities were higher across all cover types under the dependent-observer approach. Given the higher detection probabilities and associated precision combined with fewer logistical constraints, we suggest that the dependent-observer approach be used when investigators are interested in surveying birds using point counts.

Bird Populations and Habitat in Bacillus thuringiensis and Dimilin-treated and Untreated Areas of Hardwood Forest

-The objective of this study was to evaluate the effects of a gypsy moth (Lymantria dispar) infestation on nongame bird populations and habitat. This study was conducted at the Sleepy Creek Public Hunting and Fishing Area in Morgan and Berkeley counties, and Cacapon State Park in Morgan County, in the eastern panhandle of West Virginia. We compared an area that was repeatedly defoliated by the gypsy moth (Sleepy Creek) to an area (Cacapon) that was sprayed with Dimilin and Bt to control gypsy moth populations. Both areas were sampled in 1984, before defoliation or spraying, and afterwards in 1993. Tree mortality caused by gypsy moth defoliation created gaps in the canopy, increasing habitat patchiness at Sleepy Creek, but did not negatively affect total bird density. Greater habitat complexity (particularly increases in snags, windfall and shrub cover) after the gypsy moth outbreak may have increased available nesting and foraging resources for many bird species. While habitat for some flycatchers and canopy-dwelling species was reduced at Sleepy Creek, sufficient canopy was left after defoliation to support similar numbers of these birds. Despite dramatic visual effects, gypsy moth impact may not be permanently damaging to bird populations and may even be beneficial for some species. However, other factors, such as insect availability, nesting success, predation and cowbird parasitism need to be examined in gypsy moth-impacted areas to better assess effects of defoliation on bird populations.